Field of the Invention
The present invention relates to an air conditioner in which a plurality of indoor units are connected to at least one outdoor unit by refrigerant pipes and each can operate in a cooling operation mode and in a heating operation mode selectively.
Related Art
Conventionally, there is proposed an air conditioner of a so called cooling/heating free operation type in which a plurality of indoor units are connected to at least one outdoor unit by refrigerant pipes and each can operate in a cooling operation mode and in a heating operation mode selectively. For example, an air conditioner disclosed in the patent reference 1 includes an outdoor unit having a compressor, flow passage switching units, an outdoor heat exchanger and an outdoor expansion valve, three indoor units having an indoor heat exchanger and an indoor expansion valve, and a branch unit having a high pressure side indoor switch valve and a low pressure side indoor expansion valve, wherein these units are connected to each other by a high pressure gas pipe, a low pressure gas pipe and a liquid pipe to form the refrigerant circuit of the air conditioner.
The high pressure side indoor switch valve of the branch unit includes has one end connected to the high pressure pipe by a refrigerant pipe, with the other end connected to the indoor heat exchanger by a refrigerant pipe. The pressure side switch valve has one end connected to the low pressure pipe by a refrigerant pipe, with the other end connected to the indoor heat exchanger by a refrigerant pipe. By opening and closing these two kinds of indoor switch valves, the indoor heat exchanger and high pressure gas pipe can be made to communicate with each other, or, the indoor heat exchanger and low pressure gas pipe can be made to communicate with each other. In the former mutual communication, the indoor heat exchanger functions as a condenser to operate in a heating operation mode and, in the latter, the indoor heat exchanger functions as an evaporator to operate in a cooling operation mode. Therefore, by operating the respective indoor switch valves of the branch unit, the indoor units individually can operate in a heating operation mode or in a cooling operation mode selectively.
In the above air conditioner, when switching the indoor unit from the heating operation mode to the cooling operation mode, or when switching the indoor unit from the cooling operation mode to the heating operation mode, there is a fear that the refrigerant pressure of the refrigerant pipe connecting the indoor heat exchanger and branch unit can change suddenly to thereby cause the refrigerant to flow suddenly in the high pressure side indoor switch valve and low pressure side indoor switch. And, the sudden flow of the refrigerant in the high pressure side indoor switch valve and low pressure side indoor switch can cause a strange sound (refrigerant flow sound) and thus can cause a user to feel strange.
To solve such problem, in the above air conditioner, the branch unit includes a high pressure side bypass pipe connected parallel to the high pressure side indoor switch valve and having a high pressure side electromagnetic valve built therein and a low pressure side bypass pipe connected parallel to the low pressure side indoor switch valve and having a low pressure side electromagnetic valve built therein, while, using these elements, there is carried out uniform pressure control which will be described below. Specifically, when switching the indoor unit from the heating operation to the cooling operation, the high pressure side indoor switch valve and indoor expansion valve are closed and the low pressure side electromagnetic valve is opened, while leaving them in this state for a given time. Thus, the low pressure gas pipe side and indoor heat exchanger side of the low pressure side indoor switch valve are made to communicate with each other by the low pressure side bypass pipe, thereby reducing the refrigerant pressure of the indoor heat exchanger side of the low pressure side indoor switch valve. Therefore, when the low pressure side indoor switch valve is opened in order to start the cooling operation, it is possible to prevent the occurrence of the strange sound caused by the difference between the refrigerant pressures of the low pressure gas pipe side and indoor heat exchanger side of the low pressure side indoor switch valve.
When switching the indoor unit from the cooling operation to the heating operation, the low pressure side indoor switch valve and indoor expansion valve are closed and the high pressure side electromagnetic valve is opened, while leaving them in this state for a given time. Thus, the high pressure gas pipe side and indoor heat exchanger side of the high pressure side indoor switch valve are made to communicate with each other by the high pressure side bypass pipe, thereby increasing the refrigerant pressure of the indoor heat exchanger side of the high pressure side indoor switch valve. Therefore, when the high pressure side indoor switch valve is opened in order to start the heating operation, it is possible to prevent the occurrence of the strange sound caused by the difference between the refrigerant pressures of the high pressure gas pipe side and indoor heat exchanger side of the high pressure side indoor switch valve.
In the above air conditioner, during operation of the air conditioner, when a plurality of indoor units (in the air conditioner disclosed in the JP-A-H05-203275 (pages 3 to 4, and FIG. 1), three indoor units) are all stopped by an instruction from a user, an outdoor unit is also stopped, that is, a compressor provided in the outdoor unit is also stopped. From this state, also when the air conditioner starts to operate using any one of the indoor units according to an operation instruction from a user, there is operated pressure equalizing control similarly when the operation mode of this indoor unit is switched. Specifically, when the indoor unit operates in a cooling operation, the low pressure side electromagnetic valve is opened and is left opened for a given time, thereby reducing the refrigerant pressure of the indoor heat exchanger side of the low pressure side indoor switch valve. Also, for a heating operation, the high pressure side electromagnetic valve is opened and is left opened for a given time, thereby increasing the refrigerant pressure of the indoor heat exchanger side of the high pressure side indoor switch valve.
On the other hand, when a long time, for example, an hour or more has passed since the stop of the compressor, the refrigerant circuit of the air conditioner is equalized in pressure. In such pressure equalized state of the refrigerant circuit, when there is operated the pressure equalizing control in the indoor unit, the indoor unit cannot start to operate until the pressure equalizing control is ended, thereby raising a fear that the time necessary before the indoor unit starts to operate is longer than necessary and thus can impair the comfort of a user.
One or more embodiments of the present invention aims at solving the above problems and thus it is an object of the invention to provide an air conditioner which can carry out proper pressure equalizing control according to the state of a refrigerating cycle.